Prostaglandins (PGs) and thromboxanes play a fundamental role in renal physiology. PGs synthesized in the kidney are secreted into the urine by active uptake into the proximal tubule cell, followed by translocation across the luminal membrane. The molecular mechanism of renal PG transport has remained unclear. Our laboratory has identified a cDNA homologue of a recently-cloned organic anion transporter, which we call "OATP-2", that is expressed in rat kidney. When expressed in cultured mammalian cells or in Xenopus oocytes, OATP-2 catalyzes transport of PGE2 equals approximately PGF2alpha > TxB2>> 6-keto-PGF-1alpha. The Km for PGE2 is approximately 100 nM. Several classic organic anions inhibit OATP-2-mediated PG transport. Thus, OATP-2 is a novel prostaglandin transporter. The long term objective of this five-year proposal is to understand, at a molecular level, the localization, function, structure, and regulation of OATP-2, especially as these pertain to the kidney. The Specific Aims are to: l. Characterize OATP-2 mRNA expression and clone renal isoforms. 2. Immunologically characterize OATP-2 protein expression. 3. Define the fundamental transport properties of cloned rat OATP-2. 4. Initiate structure-function analysis of OATP-2. 5. Examine the regulation of OATP-2 by kinases and steroid hormones. The proposed experiments are likely to yield fundamental information about the cellular and molecular mechanisms of PG transport in the kidney and other tissues, and about organic anion transport in general.